Bench Durability Test of Shock Absorber Using the Intermittent Operation Function within the Specified Temperature Range of the Specimen [JASO C602]

Bench Durability Testing of Automotive Shock Absorbers Using EMT Series (JASO C602)

Significance of the topic

Shock absorbers are critical for vehicle ride comfort, handling stability and safety. Standardized bench durability and damping characteristic tests (JASO C602) verify performance and long-term reliability of telescopic shock absorbers under controlled mechanical and thermal loads. Reliable bench methods that maintain the specimen within a prescribed temperature window are essential because viscous damping converts kinetic energy into heat, which directly affects measured damping forces and can bias durability assessments if not controlled.

Study objectives and overview

This report demonstrates how Shimadzu’s EMT series electromagnetic fatigue testing machine and Windows Software for 4830 implement a JASO C602 bench durability test on a commercially available four-wheel rear shock absorber. The primary objective was to perform a 1 × 10^6-cycle endurance test while keeping the shock absorber temperature within the standard range (80 ± 10 °C) by using an intermittent operation function that pauses and restarts excitation based on the specimen temperature.

Methodology

• Specimen: Commercial rear shock absorber for a four-wheel vehicle (outer diameter 45 mm, no dust cover).
• Pre- and post-endurance measurements: Damping force characteristic tests at multiple excitation speeds (0.05, 0.1, 0.3 and 0.45 m/s) and ±50 mm amplitude to characterize force–stroke and force–speed behavior.
• Bench durability test: Sine displacement control at 0.45 m/s, ±25 mm amplitude, vertical orientation, 1 × 10^6 repetitions. Ambient lab temperature ~24 °C.
• Thermal management: A Type K thermocouple attached to the outer cylinder provided an analog temperature feedback to the 4830 controller. Compressed air (laboratory supply) provided external forced cooling to the outer cylinder.
• Intermittent operation: Software monitors the thermocouple signal and automatically pauses the test when specimen temperature rose above 90 °C and restarts when it dropped below 70 °C (target 80 ± 10 °C per JASO C602). This reduces the need for dedicated continuous cooling hardware.

Used instrumentation

• Electromagnetic fatigue testing machine: EMT-1kNV-50 (EMT series)
• Controller: 4830 controller with Windows Software for 4830 (intermittent operation function available since software v4.15)
• Load cell capacity: 1 kN
• Stroke capability: ±50 mm
• Fixtures: Custom shock absorber fixture with tapered clamping to eliminate rattle under tensile and compressive loads
• Temperature sensor: Type K thermocouple (outer cylinder surface)
• Cooling: Compressed air (laboratory supply)

Key test conditions (summary)

• Damping force tests: Displacement control, sine waveform, excitation speeds 0.05–0.45 m/s, ±50 mm amplitude, repetitions varying per speed.
• Durability test: Displacement control, sine waveform, 0.45 m/s excitation, ±25 mm amplitude, 1 × 10^6 cycles, specimen temperature 80 ± 10 °C maintained by intermittent operation and compressed air cooling.

Main results and discussion

• Temperature control: The intermittent operation strategy successfully kept the outer cylinder temperature within the 70–90 °C band for the full 1 × 10^6 cycles, demonstrating practical thermal control without extensive continuous-cooling hardware.
• Damping force stability: Lissajous (force–stroke) and force–speed plots before and after the endurance test showed no significant degradation. Peak extension and contraction forces at 0.3 m/s were effectively unchanged within tolerance limits. Reported values:
  • Extension: before 768.6 N → after 752.0 N
  • Contraction: before 563.8 N → after 578.0 N
• Quality/tolerance: JASO C602 defines tolerance at 0.3 m/s as ±(13% + 20 N) extension and ±(16% + 20 N) contraction. Post-test damping forces remained within the pre-test tolerance range, indicating no quality loss under the tested conditions.
• Machine capability: Higher excitation speeds above ~0.45 m/s were not tested because damping force exceeded the available test capacity; the EMT series actuator demonstrated high frequency response suitable for high-speed excitation up to the machine’s force limits.

Practical benefits and applications

• The intermittent operation function allows laboratories to comply with JASO C602 temperature requirements without investing in elaborate continuous cooling systems, reducing test setup complexity and cost.
• High actuator responsiveness of the EMT series supports dynamic testing and automated multi-speed damping characterization in a single test sequence.
• Methodology is directly applicable to QA/QC in component validation, supplier acceptance tests, and R&D for shock absorber designs where heat build-up influences performance.

Limitations and considerations

• Intermittent operation implies non-continuous loading; while acceptable for meeting thermal criteria of JASO C602, it produces cumulative time-to-completion increases due to cooling pauses.
• Actuator force limits restrict execution of some higher-speed reference tests where damping forces exceed machine capacity; selection of specimen and test ranges must consider equipment limits.
• External cooling by compressed air is effective for the tested specimen but may be insufficient for other designs or higher heat generation rates; cooling strategy should be validated per specimen.

Future trends and potential applications

• Integration of active cooling subsystems (liquid or directed air jets) into test rigs to achieve continuous operation at elevated thermal loads without intermittent pauses.
• Higher-force electromagnetic actuators or hybrid systems to expand speed and load envelopes while preserving high-frequency response.
• Real-time multi-sensor monitoring (internal oil temperature, pressure, accelerometers) and closed-loop thermal control to better replicate in-vehicle thermal dynamics.
• Digital twin and predictive maintenance models that combine bench data with vehicle usage profiles to predict service life and optimize test sequences.
• Extended standardization to incorporate intermittent thermal-control protocols and more rigorous in-situ measurement requirements.

Conclusion

The EMT-1kNV-50 electromagnetic fatigue test system, combined with the 4830 controller and the intermittent operation function in Windows Software for 4830, enabled a JASO C602 bench durability test maintaining specimen temperature within 80 ± 10 °C over 1 × 10^6 cycles. The shock absorber’s damping behavior remained within specified tolerances after testing, demonstrating that intermittent thermal control is an effective practical approach for standardized endurance testing when continuous cooling is impractical. The method supports QA, R&D and supplier validation workflows, subject to actuator capacity and appropriate cooling validation for each specimen.
References

• JASO C602: 2001 Telescopic Shock Absorbers for Suspension Systems
• Shimadzu Application News: Damping Force Characteristic Test of Suspension Struts (JASO C611), Application News No. 01-01017-EN